The black shape in this corner is the long L group. It controls more corner space than the L group, and this greatly improves its chances for survival.
This is White's best attack. She produces a somewhat strange ko in the corner. This is known as a ten thousand year ko.
This diagram is a modified one with extra liberty at a for the black group. Note that Black is unconditionally alive.
The attack by and
fails. Black has an excellent way to live - by playing at
, aiming to play at a . . .
If White answers at , Black will play at
. The result is a gote seki for Black - the same as living unconditionally when considered in terms of life and death.
( at 6)
The strongest attempt for White is to play atari at in this diagram. But Black sacrifies yet another stone at
, and takes back with
. . .
If White plays at ,
will cause White to be caught in a connect-and-die (a kind of shortage of liberties).
here won't start a ko either. After
, White at a, Black at b, it will be obvious that Black is unconditionally alive. The extra liberty comes in very handy here.
White has descended to the edge with . If Black doesn't answer, he dies unconditionally.
Black's attempt at a ko lacks liberties instead.
Note that can also be played at
.
Kanazawa Problem 18 / Solution includes this variation. creates a defect: now
is atari, making the previous diagram fail.
( at
)
Subsequently, if White plays at , Black lives with
and
.
White descends the other way. It is still the case that White to play can kill Black unconditionally.
This is also shortage of liberties. Black can't play at a after .
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